In the “v5” architecture (Activiti, Camunda, Flowable 5), the execution tree has all kinds of optimizations and reuse of scopes that makes it very hard to predict exactly what the process is by looking at its execution tree. There are some situations where a BPMN process will go into a loop and just not execute (unless you explicitly handle every diferent situation within the tangled optimizations).
With the (completed) v6 architecture, there’s no reuse of execution scopes and 1:1 mapping to BPMN and execution means these scenarios work fine.
Cheers
Paul.